This invention relates to a resist composition and a patterning process using the resist composition.
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 xcexcm or less.
For resist materials for use with a KrF excimer lasers, polyhydroxystyrene having a practical level of transmittance and etching resistance is, in fact, a standard base resin. For resist materials for use with ArF excimer lasers, polyacrylic or polymethacrylic acid derivatives and polymers containing aliphatic cyclic compounds in the backbone are under investigation. All these polymers have advantages and disadvantages, and none of them have been established as the standard base resin.
More particularly, resist compositions using derivatives of polyacrylic or polymethacrylic acid have the advantages of high reactivity of acid-decomposable groups and good substrate adhesion and give relatively satisfactory results with respect to sensitivity and resolution, but have extremely low etching resistance and are impractical because the resin backbone is weak. On the other hand, resist compositions using polymers containing alicyclic compounds in their backbone have a practically acceptable level of etching resistance because the resin backbone is robust, but are very low in sensitivity and resolution because the reactivity of acid-decomposable protective groups is extremely low as compared with those on the (meth)acrylic polymers. Poor substrate adhesion because of the too robust backbone of the resin and a likelihood of swelling due to high hydrophobicity are also problematic. These compositions are thus impractical as well.
In the prior art, attempts were also made to combine polymers of different types as a base resin. However, in many cases, particularly when polymers of different backbone structures are combined, many such polymers are not compatible with each other and do not form homogeneous resist solutions. A resist solution, if obtained, gives rise to phase separation or clouding upon coating, failing to form a satisfactory film. Even when a resist film is formed, partial stripping can occur, due to an uneven distribution of the base resins, during the patterning step.
Therefore, an object of the present invention is to provide a resist composition having a high resolution and etch resistance and useful in precise micropatterning, and a patterning process using the resist composition.
It has been found that by using as a base resin in a resist composition a hydrogenated product of a ring-opening metathesis polymer having excellent etch resistance among polymers containing an alicyclic compound in the backbone, and combining a poly(meth)acrylic acid derivative in part with it, an outstanding improvement in resolution is achievable, and the etch resistance, though experiencing a slight decline, is maintained within the practically acceptable range. When a polymer having a specific structure containing an oxygen atom within the backbone as shown by the general formula (1) below is used as the hydrogenated product of a ring-opening metathesis polymer, the polymers are more compatible with each other so that a more improvement in resolution is achievable.
In a first aspect, the invention provides a resist composition comprising a hydrogenated product of a ring-opening metathesis polymer and a poly(meth)acrylic acid derivative as a base resin.
Preferably, the hydrogenated product of ring-opening metathesis polymer is a polymer comprising recurring units of the following general formula (1) and having a weight average molecular weight of 500 to 200,000. 
Herein R1 is hydrogen, methyl or CH2CO2R3; R2 is hydrogen, methyl or CO2R3; R3 which may be identical or different between R1 and R2 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms; R4 is an acid labile group; R5 is a halogen atom, a hydroxyl group, a straight, branched or cyclic alkoxy, acyloxy or alkylsulfonyloxy group having 1 to 15 carbon atoms, or a straight, branched or cyclic alkoxycarbonyloxy or alkoxyalkoxy group having 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms; at least one of R6 to R9 is a monovalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group while the remaining R""s are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, or R6 to R9, taken together, may form a ring, and in that event, at least one of R6 to R9 is a divalent hydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxyl group while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms; at least one of R10 to R13 is a monovalent hydrocarbon group of 2 to 15 carbon atoms containing at least one partial structure selected from among ether, aldehyde, ketone, ester, carbonate, acid anhydride, amide and imide while the remaining R""s are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, or R10 to R13, taken together, may form a ring, and in that event, at least one of R10 to R13 is a divalent hydrocarbon group of 1 to 15 carbon atoms containing at least one partial structure selected from among ether, aldehyde, ketone, ester, carbonate, acid anhydride, amide and imide, while the remaining R""s are independently single bonds or straight, branched or cyclic alkylene groups of 1 to 15 carbon atoms; X1 to X3 each are independently a methylene group or oxygen atom, with the proviso that all X1 to X3 are not methylene groups at the same time; W is a single bond or a straight, branched or cyclic (p+2)-valent hydrocarbon group having 1 to 5 carbon atoms, in which at least one methylene group may be substituted with an oxygen atom to form a chain-like or cyclic ether or two hydrogen atoms on a common carbon may be substituted with an oxygen atom to form a ketone; k1 to k3 each are independently 0 or 1, p is 0, 1 or 2, xe2x80x9ca,xe2x80x9d xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d representative of compositional ratios of the corresponding recurring units are such numbers that 0 less than a less than 1, 0xe2x89xa6b less than 1, 0xe2x89xa6c less than 1 and a+b+c=1. The recurring units introduced in the respective compositional ratios xe2x80x9ca,xe2x80x9d xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d each may be of one or more types.
In a second aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition of claim 1 or 2 onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation or electron beam through a photo mask; and optionally heat treating the exposed coating and developing it with a developer.
As mentioned above, resist compositions using as a base resin polymers containing an alicyclic compound in the backbone have good etch resistance, but are far inferior in resolution to resist compositions using as a base resin poly(meth)acrylic acid derivatives, and give rise to pattern stripping due to excessive hydrophobicity and pattern disruption due to swelling. In our research to overcome these drawbacks, a hydrogenated product of ring-opening metathesis polymer having excellent etch resistance is selected among other polymers containing an alicyclic compound in the backbone, as a base resin in a resist composition, and combined in part with a poly(meth)acrylic acid derivative. It has been ascertained that an outstanding improvement in resolution is then achieved. The etch resistance, though experiencing a slight decline, is maintained within the practically acceptable range. It has also been ascertained that when a polymer having a specific structure containing an oxygen atom within the backbone as shown by the general formula (1) below is used as the hydrogenated product of ring-opening metathesis polymer, the polymers are more compatible with each other so that a more improvement in resolution is achievable.
The technique of combining polymers of plural types as the base resin is per se known in the art. However, in many cases, particularly when polymers of different backbone structures are combined, they are not fully compatible with each other and do not form homogeneous resist solutions. A resist solution, if obtained, gives rise to phase separation or clouding upon coating, failing to form a satisfactory film. Even when a resist film is formed, partial stripping can occur, due to an uneven distribution of the base polymers, during the patterning step. Therefore, the technique of combining a hydrogenated product of ring-opening metathesis polymer having a specific structure with a poly(meth)acrylic acid derivative as a base resin according to the present invention apparently has originality, superiority and inventive step over the prior art.